SLK 200 erratic idle

[Neil-gsole]

My 2005 slk200 ticks over at about 800 rpm when cold, after about 15 minutes running when the engine should be warm, the tickover starts to increase to about 1000 rpm. The warmer the engine gets the tickover increases to a maximum of 1500 rpm. Someone suggested it could be a worn switch on the throttle body and thought it is a major job to replace, best done by a main dealer. Has anyone else had similar problems.